Side Chain Elimination Enables Low-Cost Fused-Ring Acceptors and Reveals a Compact Tetrameric Structure for...

Developing low-cost, high-performance non-fullerene acceptors is crucial for the commercialization of organic solar cells (OSCs). Here, we introduce a β-side-chain-free molecular design strategy that enables the preparation of two new Y6 derivatives, JSM5 and JSM6, with substantially reduced synthetic complexity and cost. Single-crystal X-ray analysis reveals an unusual tetrameric packing, originating from the removal of the β-alkyl chains in the structure. Importantly, this packing unlocks multiple S···N intermolecular interactions between the benzothiadiazole cores, driving γ-shaped molecular conformations to establish efficient layer-by-layer 3D charge transport pathways and exhibit superior intermolecular connectivity. Consequently, remarkably high short-circuit current densities (J_SCs) of up to 28 mA cm^-2 are obtained, among the highest reported for Y-series acceptors. PM6:JSM5 and PM6:JSM6 OSCs achieve power conversion efficiencies of 17.3% and 18.0%, respectively, comparable to the state-of-the-art acceptors Y6 and BTP-eC9, while reducing acceptor material cost by approximately threefold. Cost-performance analysis further indicates that JSMs rank among the most cost-effective fused-ring acceptors within the evaluated set. This work not only introduces a new packing motif enabled by β-side chain elimination but also establishes a promising molecular design framework for high-J_SC, cost-effective fused-ring acceptors, paving the path toward commercially realizable acceptor materials.